Abrasive tools

ABSTRACT

Abrasive tool mounted endwise of a shaft of a grinding machine, comprising a rigid discoidal holder, the peripheral portion of which carries a layer of abrasive grains and has the shape of a web of small thickness formed with corrugations of large relative amplitude in order to reinforce the cohesion of the abrasive grains on the holder.

[ June 17, 1975 United 2 States Patent 1 Scandaletos Nelson.....................::...

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[30] Foreign Application Priority Data May 17, 1972 France Examiner Donald May 8 [57] ABSTRACT Abrasive tool mounted endwise of a shaft of a grinding machine, comprising a rigid discoidal holder, the peripheral portion of which carries a layer of abrasive [52] US. 51/206 NF; 51/209 R [51] Int. B24d 5/04; B24d 5/14; B24d 7/04 [58] Field of Search........ 51/206 R, 206 NF, 209 R,

grains and has the shape of a web of small thickness formed with corrugations of large relative amplitude in order to reinforce the cohesion of the abrasive grains on the holder.

[56] References Cited UNITED STATES PATENTS 51/206 R 125/15 X 51/206 R 163,880 6/1875 Morrison........................... 927,164 7/1909 Puffer....... 1,989,074 l/1935 Bullard..............................

15 Claims, 8 Drawing Figures PATEN'FEBJUH 17 1915 3,889,430 SHEET 2 PATENTEDJUN 11 SHEET 3 1 ABRASIVE TOOLS The present invention relates generally to abrasive tools or like grinding implements adapted to be cut out for instance from a vulcanized or cured fibre sheet the axial part of which comprises removable means for centering and fastening onto the shaft or onto a bearing plate mounted on the latter and the peripheral portion of which carries on at least one of its sides a layer or coating of abrasive grains or grit bonded by an adhesive.

These abrasive disks or grinding wheels are essentially used for surface finishing works such as fettling or trimming of castings or like moulded parts, flushing of weld beads or fillets, pumicing or rubbing down carriage bodies or coach work or other metal sheet structures, polishing stone or concrete, and so on.

ln these various utilizations, a rotating abrasive disk or wheel sector is applied by being laid flat onto the surface to be worked under a small angle which is however sufficient to provide for the disengagement of the opposite sector. Accordingly such an abrasive disk operates initially with its periphery which is quickly changed by wear into a slightly tapered annular active or engaging face gradually approaching the axis, thereby being effective to proportionally reduce the engaging speed of the abrasive material and to lay bare the peripheral portion of the holder. Consequently the abrasive disk is quickly put out of use and has to be replaced.

To obviate this drawback the disk or wheel should comprise a substantial thickness of abrasive material adjacent to its periphery, thereby preventing the arrangement of the abrasive disks presently made.

As a matter of fact in the prior art disks, the abrasive material is retained only by mere adhesion on the flat working surface of the holder in parallel relation to which are exerted centrifugal and tangential efforts resulting from the rotation and work, respectively, of the disk. These forces give accordingly rise to significant shear stresses tending to unstick, separate or detach the abrasive material of the holder in particular on the disk flange where the peripheral speed is the greatest.

Whatever the precautions taken to improve the adhesion or adhesiveness of the abrasive material onto the holder, for instance by embossing or impressing a checkered or goffering pattern onto the flat face of the holder or the use of a solvent adhesive enabling to partially fix or set the abrasive grains, it is thus impossible to increase the peripheral thickness of the abrasive material to a significant extent without giving rise to serious risks of burst of the disk in use or during work or at least of locally breaking off surface layers of abrasive material.

To overcome this difficulty, it has been suggested to incorporate into the abrasive layer one or several backing cloths, fabrics or like canvas serving as a reinforcement. This approach suffers from a first inconvenience that such a cloth is not nondeformable and therefore is only a partial approach to the problem involved and this in a well determined plane and not throughout the thickness of the abrasive material. A subsequent inconvenience is that a good anchoring of the reinforcing backing involves that the radial width of the layer of abrasive material be increased by extending it towards the centre of the holder which is an area where the abrasive material is of course unusable for work.

It has been proposed on the other hand, essentially for other grounds than the improvement of adhesiveness of the abrasive material onto the support or holder, to provide in the latter holes of relatively large diameter for instance on the order of one centimeter which the abrasive material enters partially and forms therefore tubular cramps providing for its local anchoring onto the holder. This approach is of course restricted by the fact that it is not possible to multiply such holes without weakening too much the strength of the holder and reducing too much the amount of abrasive material usable.

Thus none of the two stated prior techniques actually enables to provide an abrasive disk or wheel comprising a thick ring-shaped layer of abrasive material limited to the useful area of its peripheral rim.

The object of the invention is to solve this problem in a different way, namely through a particular arrangement of the peripheral or rim portion of the holder effective to retain the abrasive material no longer through mere adhesion or adhesiveness onto a flat surface but through a close or intimate imbrication of the abrasive material and holder on the major portion of the thickness of the useful disk area.

For this purpose an abrasive tool or like grinding implement according to the invention is essentially characterized in that the peripheral portion of its holder exhibits the shape of a web of small thickness comprising corrugations of large relative amplitude and possibly projections, depressions, hollows or like recesses and- /or perforations formed by moulding or casting or plastic deformation and which due to their own configuration and their whole distribution on the one hand reinforce or strengthen and/or decrease the weight of said holder and on the other hand increase its developed surface area and in particular form positive anchoring faces to provide the retention against the centrifugal and tangential forces as well as the cohesion in spite of the wear of the bonded abrasive material forming a pcripheral ring-shaped area with an average thickness several times higher than that of said web.

Preferably, said corrugations, projections, depressions and/or perforations are shaped and distributed so that at any point of the ring-shaped area the abrasive material be closely or intimately imbricated with the holder by being mutually set or interfitted into each other.

It follows obviously from such arrangements that the interface between holder and abrasive material is no longer restricted to a radial plane but on the contrary develops along the three dimensions and in particular through the thickness of the abrasive disk. It results therefrom that the surface of contact between the abrasive material and the holder is significantly multiplied and exhibits various local orientations thereby not only multiplying the adhesion of the abrasive material in proportional relationship but also enabling locally its positive anchoring onto the supporting holder. With every abrasive grain being thus in close proximity to an adhesion or abutment surface, the wear of the disk cannot cause any burst or breaking off even in the case of a thick ring-shaped area of abrasive material limited to the periphery or rim portion of the disk.

To take the best advantage of the previous arrangements, the material of the supporting holder thus closely or intimately imbricated with the abrasive layer or coating must of course be easily removable with increasing wear of the latter in operation.

To this end, and according to another characterizing feature of the invention, said corrugations, projections, depressions and/or perforations are shaped and distributed so that every annular area of the wearing or chafing surface of the ring-shaped area comprises areas of abrasive materials alternating with flushings or outcrops of the holder or of abrasive material only.

Thus the contact between the material of the holder and the worked surface is discontinuous thereby facilitating the gradual removal of said material and avoiding any risk of hard facing or clogging up of the abrasive material.

Preferably the sequence of said abrasive areas and flushings is aperiodical on the periphery of the disk so as to remove any risk of onset of vibration likely to be harmful to a good cohesion of the holder-abrasive material complex.

According to an embodiment of the abrasive tool of the invention, the peripheral portion of the holder comprises radially or spirally arranged corrugations. Moreover this peripheral portion may be drilled with holes of small diameter evenly distributed over its surface or provided with thin projections intersecting said corrugations. In the former case, the anchoring of the abrasive material on the working face of the disk may advantageously be improved by pressing onto its opposite face an abrasive material with a finer grain which enters said holes to become mixed or blended with the working abrasive material which is thereby firmly anchored onto the holder.

On the other hand such a tool exhibits accordingly on its periphery a significant body or amount of bonded abrasive material which is retained onto the holder by its base only. This may be an inconvenience in some particular cases of very heavy work since the abrasive mass located at the periphery of the tool has a tendency under the action of repeated shocks to separate from its supporting holder thereby decreasing the durability or service life of this kind of tool and exhibiting some lack of safety in the work.

In order to avoid such an inconvenience, the invention provides an abrasive tool of the kind previously described and which is characterizedin that the face of the supporting holder carrying the bonded abrasive material comprises at least one circular groove preferably located adjacent to the periphery and wherein is partially set or fitted a tubular strip of a substantially constant height one fraction of which projects outwards from the groove in parallel relation to the axis of the supporting holder, said strip made from a substantially inextensible or unstretchable material and formed with many orifices extending therethrough being embedded into the ring-shaped layer of bonded abrasive material to serve as a binding hook.

This tubular strip made from inextensible or unstretchable material thus enables to lock the body of bonded abrasive material lying at the periphery or rim of the tool and prevents it from becoming split up into fragments under the influence of shocks while being merely locked in a circular groove located preferably in the vicinity of the periphery or rim of the tool.

Moreover owing to the many orifices extending through this strip, the bonded abrasive material on the supporting holder forms a unitary or integral assembly on either side of this strip since the resin and the bonded abrasive grains on each side of this strip are moreover rigidly connected through the orifices of this strip. v

According to a further characterizing feature of the invention, said tubular strip is made from a net or cloth with large or wide meshes made from inextensible fibres such as glass fibre.

This embodiment lends itself in particular to the moulding or casting of the abrasive material onto the supporting holder and onto the strip fitted into said circular groove of the holder. A

According to still another characterizing feature of the invention, the supporting holder comprises, between said ring-shaped area of bonded abrasive material and said central part, a circular corrugation forming a yielding connection damper or like flexible shock absorber. I

Further characteristics and advantages of the invention will appear more clearly when reading the following detailed description of several non-limiting examples of embodiments illustrated by the accompanying drawings wherein:

FIG. 1 is a partial perspective view, with parts broken away, of a first embodiment of an abrasive tool according to the invention; I

FIG. 2 is a partial diagrammatic radial section of the tool of FIG. 1;

FIG. 3 is a partial radial section of a'second embodiment of a tool according to the invention;

FIG. 4 is-a partial top view, with parts broken away, of the tool of FIG. 3;

FIGS. 5 and 6 are a partial peripheral view and a partial radial section, respectively, of a third embodiment of an abrasive tool according to the invention; and

FIGS. 7 and 8 are perspective half views of alternative embodiments or modifications of a tool according to the invention.

FIGS. 1 and 2 show the structure of an abrasive tool forming a first exemplary embodiment of the invention. This tool 10 consists essentially of a holder 11 made from moulded plastics material or possibly from fibre or soft metal and shaped by being pressed or stamped. The axial portion 12 of this holder comprises means (not shown) for its centring and its fastening onto the shaft of a grinding machine or onto a hearing or backing plate fitted onto said shaft. The peripheral portion 13 forms a thin annular web provided with radial corrugations 14 of large relative height and with evenly distributed circular perforations 15 of small diameter; the corrugations 14 are substantially of a sine-wave like shape and of constant height whereas the diameter and denseness of the perforations 15 decrease gradually towards the inside of the disk.

One side face of the peripheral portion 13 of the holder 11 is covered or coated with a thick layer 16 of abrasive material bonded with a suitable adhesive and the grain of which is determined by the character of the work to be done; the opposite side face of this peripheral portion 13 is covered or coated with a relatively thinner layer 17 made from an abrasive material with finer grains. The abrasive layers 16, 17 are simultaneously bonded onto the holder 11 so that the abrasive material with finer grain penetrates through the perforations of 'the holder to become locally mixed or compounded with the abrasive working layer 16 for locking the coarser grains thereof. Thereby is achieved through mutual sealing" an intimate connection of both abrasive layers of their holder.

The radial corrugations 14 of the peripheral web 13 of the holder on the one hand reinforce the strength and in particular the bending strength under working pressure and on the other hand form sloping surfaces enabling a positive anchoring of the abrasive material against the tangential forces developed in operation. Moreover the perforations 15 formed in the peripheral web 13 of the holder on the one hand assist in decreasing its weight and on the other hand allow as already stated a positive anchoring of the abrasive working layer 16 against the centrifugal forces arising from the fast rotation of the disk as well as against the tangential forces and the pressure and bending forces which are imparted in operation. In addition the corrugations 14 like the perforations 15 increase the developed surface of the peripheral web 13 and extend it to a significant fraction of the aggregate thickness of the abrasive layers l6, 17 every grain of which is thus positioned in close proximity to an adhesion or bonding surface and- /or an anchoring structure. It results from the combined effect of these different arrangements a close im brication and an interfitting relationship of the abrasive material and of the holder material throughout substantially the whole bulk of the peripheral ring-shaped or rim working portion which thus forms a coherent and a strong construction. It follows therefrom that the gradual wear of the disk is not likely at all events to result in its burst or even local breaking away of abrasive material on its surface.

Moreover the particular configuration of the peripheral portion of the holder results in each annular area of the wearing or chafing surface of the disk alternately exhibiting regions of active abrasive material and flushings of passive material of the holder which may thus be easily removed through abrasion and/or local breaking off as the wear increases without any risk of smoothing or hard facing or clogging up of the abrasive material or overheating of the work piece being worked.

FIGS. 3 and 4 show another embodiment of the invention, namely an abrasive disk 20 comprising a supporting holder 21 made from plastics material moulded or cast over a previously bonded ring-shaped portion of abrasive material. The central portion of the holder 21 forms a relatively thick fastening tray 22 whereas its peripheral portion 23 is in the shape of a thin web provided with spirally arranged corrugations 24. Across these corrugations on the working face or side of the disk extend thin partitions or like ribs 25 of irregular shape and aperiodical distribution on the periphery of the disk. On this working side is bonded a thick layer of abrasive material 26 the root or base of which is closely fitted in accommodating recesses defined by the corrugations 24 and the partitions 25. In the apparent face of the abrasive layer are desirably impressed flutes or serrations 27 preferably arranged in spiral relationship and in corresponding relation with the corrugations 24 so that the useful average or mean thickness of the abrasive material be substantially constant. Lastly, the plastics material of the holder 21 desirably forms on the outer rim portion of the abrasive layer a skirt 28 adapted to improve the appearance of the shop-new disk and to facilitate handling and storage thereof.

FIGS. 5 and 6 illustrate a third alternative embodiment or modification of an abrasive tool according to the invention wherein the holder is divided into a pair of parts, namely a centring and fastening hub 31 and an annular peripheral portion 32; the latter consists of a grid made from punched or cut-out or expanded metal or from some other suitable rigid material, wherein are formed through deep drawing, pressing or like stamp ing corrugations 33 arranged in radial or spiral relationship. The inner periphery of this grid 32 is made fast with the hub 31 by being fitted on dogs or like stud pins 34 formed on the periphery of the latter, the whole as sembly being embedded into a thick peripheral ringshaped coating of bonded abrasive material 35. Such an arrangement offers the particular advantage of enabling the making of a large variety of abrasive disks by using the same hub hence the same mould.

The abrasive tool shown in FIG. 7 consists essentially of a holder 50 made from moulded plastics material and possibly from fibre or soft metal and shaped by being pressed, deep drawn or stamped. The central portion 51 comprises means, not shown, for centring and fastening onto the shaft of a grinding machine and its peripheral portion 52 provides a thin annular web the side face of which carrying the bonded abrasive material 53 comprises means 54 such as circular projecting or raised ribs and a groove 55 preferably located adjacent to its periphery.

The circular ribs 54 provide a positive anchoring of the abrasive material 53 with its base onto the corresponding side face of the holder whereas the groove 55 is adapted to accommodate a tubular strip 56 which in this form of embodiment is made from a wide-mesh cloth, fabric or like canvas made from glass fibre which extend in parallel relation to the axis of rotation of the tool. This strip 56 is partially fitted or set into the circular groove 55 while being entirely embedded into the body of bonded abrasive material. The latter, which is moulded or cast onto the holder when the strip 56 is positioned within the groove 55, forms an integral or unitary assembly since the resin and abrasive grains are bonded together on either side of this tubular strip and across thereof or therethrough.

The holder 50 also comprises between its central portion 51 and its peripheral portion 52 a corrugation 57 which enables simultaneously to bound towards the in' side of the ring-shaped layer of abrasive material 53 and to form a flexible or yielding vibration and connection damper or shock absorber between the body of abrasive material 53 and the central part 51 of the holder to compensate for any want of balance, warping or untrue condition or centring defect of the ringshaped layer of abrasive material.

Moreover owing to positive anchoring of the abrasive material onto the holder by means of the strip or grid 56, it is possible to use a body of abrasive material much larger than on the prior art disks and which is distributed so that its thickness gradually increases from the corrugation 57 to the periphery of the holder 50.

substantially flat whereas the peripheral part of the holder forms a frusto-conical surface with an angle in the range of the angle of attack of the disk in operation.

In FIG. 8 has been shown an alternative embodiment of the tool of FIG. 7 wherein the holder 60 comprises on its periphery a pair of circular concentric grooves 61 and 62 in each of which is accommodated a tubular grid 63, 64 extending in parallel relation to the axis of rotation of the tool and fully embedded into the bonded abrasive material 65. This arrangement of both coaxial grids enables to additionally reinforce the anchoring of the abrasive material on the holder and to increase its resistance to shocks even during particularly heavy work.

It results clearly from the preceding specification that the invention allows to provide abrasive disks or wheels exhibiting considerable advantages over prior art disks. While all theknown abrasive disks have an essentially flat interface between holder and abrasive material and accordingly the layer of abrasive material is not retained by mere adhesiveness and therefore is necessarily wide and thin, the invention owing to the positive securement of the abrasive material over a large portion of its thickness enables to provide disks comprising a thick peripheral ring-shaped coating of abrasive material radially restricted to the useful area corresponding to adequate peripheral speeds. This ring-shaped coating of course includes for an equal surface an amount of abrasive material well above that a disk of conventional construction may exhibit. The abrasive material being firmly anchored or strongly secured onto the holder is not necessarily bonded under a high pressure and may therefore exhibit an open" structure improving its bite. The apparent face of the thick ringshaped coating of abrasive material may comprise deep grooves or serrations contributing to increase the aggressiveness of the disk and to facilitate the ventilation of the tool and of the surface being worked as well as the discharge of the scrap removed through abrasion. Finally the combination of the anchoring means described and in particular the use of one or both tubular strips fitted or set into grooves of the holder enables to achieve a service life and a reliability of the abrasion tools which are definitely higher than those of the prior art tools.

It should be understood that the invention is not at all limited to the embodiments described and shown herein which have been given by way of example only; on the contrary the invention comprises all the means forming technical equivalents of those described and illustrated as considered either separately or in combination with each other and used within the scope of the appended claims.

What is claimed is:

1. In an abrasive tool adapted to be mounted endwise of the shaft of a grinding machine rotatable at a high speed which tool includes a central support section of discoidal shape adapted to be centered upon and se-v cured to said shaft and a peripheral section carrying on one of the side faces thereof a coating of abrasive granular material bonded by an adhesive presenting a generally radially extending working surface, the improvement comprising said peripheral section of said support being a relatively thin radially extending web having a thickness in the axial direction substantially less than that of said central support section, the region between said web and said central support section defined by the thickness difference of said web and supportbeing covered by said coating of abrasive material, at least a' portion of said surface of said web having undulations of amplitudegreater than the thickness of said web to provide an increase in surface area, and anchoring faces for increased retention of said coating of abrasive material, said undulations also serving to provide reinforcement of said coating against centrifugal and tangential forces which develop during operation of said machine. v

2. An abrasive tool according to claim 1 wherein said undulations comprise radially extending corrugations, said web having a plurality of apertures formed therethrough, one of the side faces of said web being covered with a coating of a first abrasive granular material and the opposite face of said web being covered with a thinner coating of a second more finely grained abrasive material, said more finely grained material extending through said apertures to intermix with said first abrasive material and form a bond therewith.

' 3. An abrasive tool according to claim 2, wherein the size and number of apertures formed in said web decrease in the direction of said central support section.

4. An abrasive tool according to claim 3, wherein said central support section is thick relative tosaid peripheral section, said peripheral section being provided with spirally extending corrugations and a plurality of upstanding irregularly shaped partitions which extend across said corrugations and define together with said corrugations a plurality of recesses, said coating of abrasive material filling said recesses down to the bases of said partitions and their intersection with said corrugations. v

5. An abrasive tool according to claim 4, wherein the working face of said coating of abrasive material is formed with spiral serrations arranged to provide a substantially constant thickness of said coating throughout said web.

6. An abrasive tool according to claim 1, wherein said central support section and said peripheral web are separately formed and detachably connected.

7. An abrasive tool according to claim 6, wherein saidundulations are corrugations formed in the web which extend in a generally radial direction, the periphery of said central support section being provided with a plurality of upstanding pin elements adapted to cooperate with cooperable means carried by said web to detachably connect said web and central support section.

8. An abrasive tool according to claim 7, wherein said corrugations extend in a spiral pattern.

9. An abrasive tool according to claim 1, wherein said peripheral section is formed with a plurality of concentric raised ribs and with an annular groove located adjacent the periphery thereof, a tubular member being positioned within said annular groove projecting into and being embedded in said coating of abrasive material, said central support section being provided with a raised corrugation which defines the inner circumferential boundary of said coating of abrasive material, said raised corrugation serving as a shock absorber between the mass of abrasive material and said central support section to compensate for unbalanced forces acting upon said mass of abrasive material during operation of the machine.

10. An abrasive tool according to claim 9, wherein 11. An abrasive tool according to claim 9, wherein a pair of said annular grooves are provided and a tubular member is positioned within each of said grooves.

- 12. An abrasive tool according to claim 11, wherein said tubular members are made of a material selected from wide-mesh cloth, fabric and fibre glass canvas.

13. An abrasive tool according to claim 9, wherein the thickness of said coating of abrasive material increases from said raised corrugation to the outer periphery of said peripheral section, the outer surface of said coating being substantially flat whereas the surface of said peripheral section slopes downwardly in a radially outward direction.

14. An abrasive tool according to claim 11, wherein the thickness ofsaid coating of abrasive material increases from said raised corrugation to the outer periphery of said peripheral section, the outer surface of said coating being substantially fiat whereas the surface of said peripheral section slopes downwardly in a radially outwardly direction.

15. In an abrasive tool adapted to be mounted endwise of the shaft of a grinding machine rotatable at a high speed which tool includes a central support section of discoidal shape adapted to be centered upon and secured to said shaft and a peripheral section carrying on one of the side faces thereof a coating of abrasive granular material bonded by an adhesive presenting a generally radially extending working surface, the improvement comprising said peripheral section of said support being a relatively thin radially extending web, at least a portion of the surface of said web being undulated to provide an increase in surface area, and anchoring faces for increased retention of said coating of abrasive material, said undulations also serving to provide reinforcement of said coating against centrifugal and tangential forces which develop during operation of said machine, said coating having a thickness at approximately the mid-point of its radial extent substantially greater than the thickness of said web, said central support section being thick relative to said periph eral section, said peripheral section being provided with spirally extending corrugations and a plurality of upstanding irregularly shaped partitions which extend across said corrugations and define together with said corrugations a plurality of recesses, said coating of abrasive material filling said recesses down to the bases of said partitions and their intersection with said corru- 

1. In an abrasive tool adapted to be mounted endwise of the shaft of a grinding machine rotatable at a high speed which tool includes a central support section of discoidal shape adapted to be centered upon and secured to said shaft and a peripheral section carrying on one of the side faces thereof a coating of abrasive granular material bonded by an adhesive presenting a generally radially extending working surface, the improvement comprising said peripheral section of said support being a relatively thin radially extending web having a thickness in the axial direction substantially less than that of said central support section, the region between said web and said central support section defined by the thickness difference of said web and support being covered by said coating of abrasive material, at least a portion of said surface of said web having undulations of amplitude greater than the thickness of said web to provide an increase in surface area, and anchoring faces for increased retention of said coating of abrasive material, said undulations also serving to provide reinforcement of said coating against centrifugal and tangential forces which develop during operation of said machine.
 2. An abrasive tool according to claim 1 wherein said undulations comprise radially extending corrugations, said web having a plurality of apertures formed therethrough, one of the side faces of said web being covered with a coating of a first abrasive granular material and the opposite face of said web being covered with a thinner coating of a second more finely grained abrasive material, said more finely grained material extending through said apertures to intermix with said first abrasive material and form a bond therewith.
 3. An abrasive tool according to claim 2, wherein the size and number of apertures formed in said web decrease in the direction of said central support section.
 4. An abrasive tool according to claim 3, wherein said central support section is thick relative to said peripheral section, said peripheral section being provided with spirally extending corrugations and a plurality of upstanding irregularly shaped partitions which extend across said corrugations and define together with said corrugations a plurality of recesses, said coating of abrasive material filling said recesses down to the bases of said partitions and their intersection with said corrugations.
 5. An abrasive tool according to claim 4, wherein the working face of said coating of abrasive material is formed with spiral serrations arranged to provide a substantially constant thickness of said coating throughout said web.
 6. An abrasive tool according to claim 1, wherein said central support section and said peripheral web are separately formed and detachably connected.
 7. An abrasive tool according to claim 6, wherein said undulations are corrugations formed in the web which extend in a generally radial direction, the periphery of said central support section being provided with a plurality of upstanding pin elements adapted to cooperate with cooperable means carried by said web to detachably connect said web and central support section.
 8. An abrasive tool according to claim 7, wherein said corrugations extend in a spiral pattern.
 9. An abrasive tool according to cLaim 1, wherein said peripheral section is formed with a plurality of concentric raised ribs and with an annular groove located adjacent the periphery thereof, a tubular member being positioned within said annular groove projecting into and being embedded in said coating of abrasive material, said central support section being provided with a raised corrugation which defines the inner circumferential boundary of said coating of abrasive material, said raised corrugation serving as a shock absorber between the mass of abrasive material and said central support section to compensate for unbalanced forces acting upon said mass of abrasive material during operation of the machine.
 10. An abrasive tool according to claim 9, wherein said tubular member is made of a material selected from wide-mesh cloth, fabric and fibre glass canvas.
 11. An abrasive tool according to claim 9, wherein a pair of said annular grooves are provided and a tubular member is positioned within each of said grooves.
 12. An abrasive tool according to claim 11, wherein said tubular members are made of a material selected from wide-mesh cloth, fabric and fibre glass canvas.
 13. An abrasive tool according to claim 9, wherein the thickness of said coating of abrasive material increases from said raised corrugation to the outer periphery of said peripheral section, the outer surface of said coating being substantially flat whereas the surface of said peripheral section slopes downwardly in a radially outward direction.
 14. An abrasive tool according to claim 11, wherein the thickness of said coating of abrasive material increases from said raised corrugation to the outer periphery of said peripheral section, the outer surface of said coating being substantially flat whereas the surface of said peripheral section slopes downwardly in a radially outwardly direction.
 15. In an abrasive tool adapted to be mounted endwise of the shaft of a grinding machine rotatable at a high speed which tool includes a central support section of discoidal shape adapted to be centered upon and secured to said shaft and a peripheral section carrying on one of the side faces thereof a coating of abrasive granular material bonded by an adhesive presenting a generally radially extending working surface, the improvement comprising said peripheral section of said support being a relatively thin radially extending web, at least a portion of the surface of said web being undulated to provide an increase in surface area, and anchoring faces for increased retention of said coating of abrasive material, said undulations also serving to provide reinforcement of said coating against centrifugal and tangential forces which develop during operation of said machine, said coating having a thickness at approximately the mid-point of its radial extent substantially greater than the thickness of said web, said central support section being thick relative to said peripheral section, said peripheral section being provided with spirally extending corrugations and a plurality of upstanding irregularly shaped partitions which extend across said corrugations and define together with said corrugations a plurality of recesses, said coating of abrasive material filling said recesses down to the bases of said partitions and their intersection with said corrugations. 